Tire Composition Using Elastomer Composite Blends

ABSTRACT

A process for preparing a tire comprising a rubber composition based on at least an elastomer composite, wherein the elastomer composite is prepared by a method comprising: feeding a continuous flow of a first fluid comprising a first elastomer latex to a mixing zone of a coagulum reactor; feeding a continuous flow of a second fluid comprising a second elastomer latex to the mixing zone; feeding a continuous flow of a third fluid comprising a particulate filler slurry to the mixing zone; allowing the first elastomer latex and the second elastomer latex to coagulate with the particulate filler; and discharging a flow of elastomer composite from a discharge end of the coagulum reactor, wherein the first elastomer latex and the second elastomer latex are incompatible.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 13/497,026 filed Jul. 23, 2012 which claims priority under 35 USC §371 of PCT application No. PCT/US10/002514, filed on Sep. 16, 2010. Priority is also claimed of U.S. Provisional application No. 61/276,842 filed Sep. 17, 2009, the entire content of which is hereby incorporated by reference

FIELD OF THE INVENTION

This invention pertains to elastomer composites including a blend of elastomers, and methods of making such composites. More particularly, this invention concerns a process for making a tire comprising rubber compositions based on such elastomer composites.

DESCRIPTION OF THE RELATED ART

In order to obtain the optimum reinforcement properties imparted by a filler in a tire tread and thus high wear resistance, it is known that this filler should generally be present in the elastomeric matrix in a final form which is both as finely divided as possible and distributed as homogeneously as possible. Now, such conditions can only be obtained insofar as this filler has a very good ability firstly to be incorporated into the matrix during mixing with the elastomer and to be disagglomerated, and secondly to be dispersed homogeneously in this matrix.

Since fuel economies and the need to protect the environment have become priorities, it has proved necessary to produce tires having reduced rolling resistance, without adversely affecting their wear resistance. To improve the dispersion of filler into the elastomeric matrix, numerous solutions have been proposed, some of them proposing the use of masterbatches including elastomer and filler.

It is common to produce a masterbatch, that is, a premixture of filler, elastomer and various optional additives, such as extender oil. Carbon black masterbatch, for example, is prepared with different grades of commercially available carbon black which vary both in surface area per unit weight and in structure, which describes the size and complexity of aggregates of carbon black formed by the fusion of primary carbon black particles to one another.

There are a variety of methods for producing masterbatch. In one method, disclosed in U.S. Pat. No. 6,048,923, the contents of which are incorporated by reference herein, a continuous flow of a first fluid including an elastomer latex is fed to the mixing zone of a coagulum reactor. A continuous flow of a second fluid including a carbon black slurry is fed under pressure to the mixing zone to form a mixture with the elastomer latex. The mixing of the two fluids is sufficiently energetic to substantially completely coagulate the elastomer latex with the carbon black prior to a discharge end of the coagulum reactor. As disclosed in U.S. Pat. No. 6,929,783, the coagulum may then be fed to a dewatering extruder.

For some applications, it is desirable to employ blends of elastomers to optimize the mechanical properties of the masterbatch and/or a vulcanized rubber composition including such masterbatch. Blends of elastomers may be produced by dry-mixing two polymers together. Alternatively, blends may be produced by co-coagulating a mixture of elastomer latices (see, e.g., U.S. Pat. No. 4,271,213) or by recovering a polymer blend from a mixture of an elastomer latex and a solution containing a second polymer (see, e.g., U.S. Pat. No. 5,753,742). However, none of these references disclose a wet masterbatch method of combining a filler with two or more elastomers. Rather, the polymer blends produced by these methods may be dry mixed with filler to form a masterbatch. However, dry mixing can reduce polymer molecular weight and degrade polymer properties.

U.S. Pat. No. 6,521,691 discloses a wet masterbatch method in which two polymer emulsions and a filler slurry may be combined and then coagulated to form a masterbatch. Similarly, U.S. Pat. No. 6,800,126 discloses that carbon black aggregates may be blended with an oil and a low-molecular weight elastomer latex to form a pre-blend, which preblend may be combined with an emulsion of a diene-based elastomer. A composite of the elastomer and the carbon black is then recovered from the mixture. U.S. Pat. No. 4,578,411 discloses a method in which an elastomer latex, an elastomer solution, and a filler are combined, following which a composite of the two elastomers with the filler is recovered. However, all of these references disclose the combination of the filler with the elastomer and the coagulation of the latex as separate processing steps. Between these two process stages, the filler can flocculate in the emulsion to the detriment of its even distribution in the final composite.

U.S. Pat. No. 6,048,923 discloses a wet masterbatch method in which coagulation ensues upon introduction of a filler slurry to an elastomer latex, resulting in superior dispersion of filler within the elastomer composite. No coagulant is required to form this “wet mix” elastomer composite. The '923 patent discloses that blends of elastomer latices may be combined with the filler slurry to form a coagulum. However, because natural rubber latex is essentially a biological material, it contains a number of dissolved substances such as magnesium, potassium, phosphate, and sulfate ions, fatty acids, amino acids, carbohydrates, peptides, etc. The high ionic strength of the aqueous carrier can cause synthetic latices with which natural rubber latex is combined to coagulate before the filler slurry is introduced to the elastomer latex blend. Such synthetic latices are said to be incompatible with natural rubber latex. While it is possible to render the two latices compatible by adding surfactant to either the synthetic or the natural latex, the additional surfactant makes the latex more difficult to coagulate and increases the concentration of surfactant in the final rubber product. Thus, it is desirable to have a method of producing elastomer composite masterbatches incorporating a blend of materials that is not susceptible to the problem of early coagulation but which still results in a homogeneous dispersion of filler within the elastomer.

SUMMARY OF THE INVENTION

One aspect of the present invention is directed to a process for preparing a tire comprising a rubber composition based on at least an elastomer composite, wherein the elastomer composite is prepared by a method comprising: feeding a continuous flow of a first fluid comprising a first elastomer latex to a mixing zone of a coagulum reactor; feeding a continuous flow of a second fluid comprising a second elastomer latex to the mixing zone; feeding a continuous flow of a third fluid comprising a particulate filler slurry to the mixing zone; allowing the first elastomer latex and the second elastomer latex to coagulate with the particulate filler; and discharging a flow of elastomer composite from a discharge end of the coagulum reactor, wherein the first elastomer latex and the second elastomer latex are incompatible.

The first elastomer latex may include natural rubber latex, and the second elastomer latex may include a synthetic elastomer latex. The particulate filler may include carbon black. The first fluid and the second fluid may combine with the third fluid to form a mixture, and the first fluid and the second fluid may combine with the third fluid substantially simultaneously. Alternatively, the first fluid and the third fluid may combine to form a mixture, and the second fluid may combine with the mixture. The first elastomer latex and the second elastomer latex may be incompatible.

The elastomer composite used for said tire composition, may include natural rubber and about 1 to about 36 wt % styrene-butadiene rubber, for example about 20 to about 36 wt % styrene-butadiene rubber with respect to the total rubber content. The elastomer composite may exhibit a macrodispersion of less than 0.1% undispersed area.

Another aspect of the present invention is directed to a process for preparing a tire tread having a rubber composition based on at least an elastomer composite, wherein the elastomer composite is prepared by a method comprising: feeding a continuous flow of a first fluid comprising a first elastomer latex to a mixing zone of a coagulum reactor; feeding a continuous flow of a second fluid comprising a second elastomer latex to the mixing zone; feeding a continuous flow of a third fluid comprising a particulate filler slurry to the mixing zone; allowing the first elastomer latex and the second elastomer latex to coagulate with the particulate filler; and discharging a flow of elastomer composite from a discharge end of the coagulum reactor; wherein the first elastomer latex and the second elastomer latex are incompatible.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described with reference to the several drawings, in which,

FIG. 1 is a schematic diagram of an apparatus for producing elastomer composite blends according to an exemplary embodiment of the invention.

FIGS. 2A and 2B are schematic diagrams of apparatus for injection of a second elastomer latex into a coagulum according to an exemplary embodiment of the invention.

FIG. 3 is a schematic diagram of a top view of the apparatus depicted in FIGS. 2A and 2B.

FIG. 4 is a schematic diagram illustrating the configuration of samples for electrical resistivity testing.

FIG. 5 is a graph of the natural log of resistivity with respect to loading levels of N234 carbon black comparing vulcanized elastomer composite blends produced according to an exemplary embodiment of the invention (triangles, numbers indicate the proportion of styrene-butadiene rubber by weight with respect to total rubber) to vulcanized elastomer composites produced from natural rubber latex via a wet masterbatch method (diamonds), vulcanized elastomer composite blends produced from natural rubber and styrene-butadiene rubber via a dry mixing method (stars), and vulcanized elastomer composites produced from natural rubber latex via a dry mixing method (squares).

DETAILED DESCRIPTION OF THE DRAWINGS

In one embodiment, an tire comprises a rubber composition which is based on an elastomer composite which is prepared by feeding a continuous flow of a first fluid comprising a first elastomer latex to a mixing zone of a coagulum reactor, feeding a continuous flow of a second fluid comprising a second elastomer latex to the mixing zone, feeding a continuous flow of a third fluid comprising a particulate filler slurry to the mixing zone, allowing the first elastomer latex and the second elastomer latex to coagulate with the particulate filler, and discharging a flow of elastomer composite from a discharge end of the coagulum reactor. We have found that this method allows the production of elastomer composite blends, for example, blends of natural rubber latex and styrene-butadiene copolymers, from incompatible polymer emulsions.

Accordingly, said rubber composition may be used for the tread portion, sidewalls, wire skim and/or carcass.

Characterization of Particle Distribution in Filled Vulcanizates

Improvements in rubber reinforcement are reflected in the ratio of the stresses at different elongations. For carbon black-filled vulcanizates, stresses at given elongations reflect, among other things, the effect of filler morphology (particle size and structure) and surface activity, which determines filler-polymer and aggregate-aggregate interaction. The ratio of the stress at 300% elongation to that at 100% elongation, T300/T100, provides a useful approach for quantifying the degree of polymer-filler interaction because the factors governing the stresses at different elongations are different. Structure affects the occlusion of rubber in the filler aggregates. Increased occlusion increases the effective filler volume fraction, a description of the extent to which filler actually interacts with the rubber matrix and influences the properties of the rubber matrix composite, and thus the stresses at given elongations for the filled vulcanizate. For two compounds prepared with the same polymer and filled with the same carbon black at the same loading level or volume fraction, the effects of structure and surface area on stress should be the same. As a result, any difference in stresses at different strains can be attributed to the crosslinking density of the polymer matrix, polymer-filler interaction, and aggregate-aggregate interaction, the last of which leads to filler agglomeration. At low strain, the agglomerates are not broken down, and the rubber trapped in the agglomerates can be treated as filler. This increases the effective volume of the fillers, thus increasing the stress at a given elongation (i.e., strain). The filler agglomerates gradually break with increasing strain so that the effect of filler agglomeration on stress at given elongation will decrease and finally disappear at about 100% elongation. On the other hand, at higher elongation, e.g., at 300% elongation, a different mechanism is involved. In the absence of interaggregate association, the interaction between the polymer and filler has a greater influence on the stress. Where the interaction between the polymer and the filler is weak, high strain leads to slippage and deattachment (dewetting) of rubber molecules on the black surface, reducing stress for a given strain. The effect of cross-link density on stress is the about the same at both 100% and 300% strain. As a result, the ratio T300/T100 provides a measure of the in-rubber polymer-filler interaction (S. Wolff and M.-J. Wang, Rubber Chem. Technol., 65, 329 (1992)).

We have also found that improvements to the filled rubber are reflected in the microstructure of the composite. As described in U.S. Pat. No. 6,048,923, rubber composites produced by the method disclosed therein exhibit improved macrodispersion of filler with respect to dry mixed rubbers. Macrodispersion, as indicated by percent undispersed area D(%), describes the dispersion of filler within a composite at length scales of 10 microns or greater. Without being bound by any particular theory, it is believed that good macrodispersion results from the breakup of filler pellets and the uniform distribution of the resulting material within the elastomer matrix. We have found that improvements in the distribution of filler with respect to shorter length scales are correlated with improvements in the mechanical properties of the bulk product. This feature of the composite microstructure is termed microdispersion. Without being bound by any particular theory, it is believed that improvements in microdispersion result from better separation of individual filler aggregates and/or small clusters of aggregates (i.e., agglomerates) within the composite.

As used herein, the term “aggregate” refers to the smallest dispersible unit of the filler. For example, carbon black aggregates are made up of primary particles of carbon black and generally cannot be broken into smaller pieces by mechanical forces. As used herein, the term “agglomerate” refers to a plurality of aggregates in physical contact with one another and held together by physical forces. These agglomerates may be broken by mechanical forces into smaller units or particles; the smaller units may be aggregates, smaller agglomerates, or both.

The difference in conductivity between carbon black and rubber may be exploited to characterize microdispersion in carbon black—rubber composites. The conductivity of such composites depends primarily on the concentration and morphology (e.g., surface area, particle size, and structure) of the carbon black. In addition, the conductivity of these composites is influenced by the state of dispersion of the carbon black in the rubber matrix. The conductivity of a carbon black—rubber composite first increases, then decreases as the carbon black becomes more dispersed in the matrix (A. I. Medalia, “Electrical Conduction in Carbon Black Composites,” Rubber Chemistry and Technology, 1986, Vol. 59, p. 432). The initial increase is attributed to the increasing distribution and dispersion of larger carbon black agglomerates, thereby decreasing the average distance between particles in the composite. Further improvements in dispersion lead to a decrease in conductivity. As noted above, this is attributed to the separation of small groups of individual carbon black aggregates within the system (Medalia, 1986).

In certain embodiments, a wet mix elastomer composite is prepared from natural rubber and carbon black. When the elastomer composite is processed using a standardized method, CTV Method 1 (defined below), the resulting vulcanized wet mix elastomer composite exhibits a resistivity satisfying ln(resistivity)≧−0.1(loading)+x, where x is 14. Alternatively or in addition, the resistivity may also satisfy ln(resistivity)≧−0.1(loading)+x, where x is 14.5. In addition, the resistivity may satisfy ln(resistivity)≦−0.1(loading)+y, where y is 17. Alternatively or in addition, y may be 16. Alternatively or in addition, the vulcanized wet mix elastomer composite exhibits a resistivity that is at least about 2.9 times higher, for example, at least about 3.5 times higher, at least about 4 times higher, at least about 4.5 times higher, or at least about 5 times higher than the resistivity of a vulcanized dry mix elastomer composite having the same composition and prepared using a comparative method, CTV Comparative Method 1 (defined below). For example, the resistivity may be from about 3 times to about 6 times higher, from about 4 times to about 5 times higher, from about 2 times to about 5.5 times higher, or from about 2.5 times to about 4.5 times higher for the vulcanized wet mix composite than for the vulcanized dry mix composite. In any of these embodiments, the wet mix elastomer composition may include less than 2 phr of surfactant, for example, less than 1.5 phr of surfactant, less than 1 phr of surfactant, less than 0.75 phr of surfactant, less than 0.5 phr of surfactant, or from 0.25 to 2 phr of surfactant.

As used herein, CTV Method 1 means compounding a masterbatch in a 1.6 L Banbury mixer using the formulation in Table 1 and the procedure in Table 2. After each Banbury mixing stage, compounds are sheeted on a 2-roll mill operated at ambient temperature and about 40 rpm with a nip gap of about 2 mm using 4 cross-cuts and 2 end-rolls, with a rest time between stage 1 and stage 2 mixing from 4-6 hours. Compounds are then cured in a press at 150° C. using a mold with a 2 mm thick spacer for a time determined by a conventional rubber rheometer (i.e., T90+10% of T90).

TABLE 1 Ingredient Phr Rubber 100 ZnO 4 Stearic acid 2 6PPD* (antioxidant) 1.5 TBBS** (accelerator) 0.8 Sulfur 1.2 *N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine **N-tert-butyl-2-benzothiazolesulphenamide

TABLE 2 Time (min) Operation Stage 1 Farrel BR Banbury mixer (1600 cc), 75% fill factor, 80 rpm, 60° C. 0 Add rubber-carbon black masterbatch 1 Add zinc oxide, stearic acid and 6PPD 1.5 Sweep 2.5 Dump Roll mill using 4 cross-cuts and 2 end rolls Stage 2 Farrel BR Banbury mixer (1600 cc), 65% fill factor, 60 rpm, 50° C. 0 Add stage 1 compound, sulfur and accelerator 1 Dump Roll mill using 4 cross-cuts and 2 end rolls

As used herein, CTV Comparative Method 1 means preparing a vulcanized elastomer composite in a 1.6 L Banbury mixer using the formulation in Table 1 and the procedure in Table 3. After each Banbury mixing stage, compounds are sheeted on a 2-roll mill operated at ambient temperature and about 40 rpm with a nip gap of about 2 mm using 4 cross-cuts and 2 end-rolls, with a rest time between stage 1 and stage 2 mixing from 4-6 hours. Compounds are then cured in a press at 150° C. using a mold with a 2 mm thick spacer for a time determined by a conventional rubber rheometer (i.e., T90+10% of T90).

TABLE 3 Stage 1 Fill factor (%) 75 Rotor speed (rpm) 80 Start temperature (° C.) 60 Time NR addition (s) 0 Time CB addition (s) 30 Time smalls addition (s) 150 Time for sweep (s) 60, 180 Dump time (s) 240 Stage 2 Fill factor (%) 65 Rotor speed (rpm) 60 Start temperature (° C.) 50 Time masterbatch and curatives (s) 0 Dump time (s) 60

Handling of the vulcanized compounds can affect resistivity. To avoid skewing test results, the compounds should not be stored under conditions of high humidity or high temperature (e.g., greater than about 30 or 40° C.) for extended periods of time, nor should they be significantly mechanically deformed.

Wet mix elastomer composite blends prepared according to certain embodiments of the invention exhibit a ratio of T300 to T100 that is at least about 18% greater than the same ratio for a vulcanized dry mix elastomer composite blend having the same composition. For example, the ratio T300/T100 may be at least about 20% greater, at least about 25% greater, at least about 30% greater, or at least about 35% greater for a vulcanized wet mix elastomer blend than for a dry mix elastomer composite blend. Alternatively or in addition, the ratio T300/T100 may be from about 20% to about 30% greater, from about 25% to about 35% greater, from about 30% to about 40% greater, or from about 35% to about 45% greater for a wet mix elastomer composite blend than for a dry mix elastomer composite blend. In any of these embodiments, the wet mix elastomer composition may include less than 2 phr of surfactant, for example, less than 1.5 phr of surfactant, less than 1 phr of surfactant, less than 0.75 phr of surfactant, less than 0.5 phr of surfactant, or from 0.25 to 2 phr of surfactant.

As used herein, the term “wet mix elastomer composite blend” refers to an elastomer composite blend which has been prepared by a wet masterbatch process. In contrast, the term “dry mix elastomer composite blend” refers to an elastomer composite blend which has been prepared by combining two dry elastomers (e.g., less than 1% water) and particulate filler in powder form or by combining dry elastomer with an elastomer masterbatch.

Preparation of Elastomer Composite Blends

As shown in FIG. 1, a particulate filler slurry is fed into a mixing portion 10 of a coagulum reactor 11 via a filler feed line 12. A first elastomer latex is fed into mixing portion 10 via first latex feed line 14. A second elastomer latex is fed into mixing portion 10 via second latex feed line 16. The two latices coagulate in the mixing portion 10, and the coagulum, including both elastomers and particulate filler, proceeds through a diffuser portion 17 of coagulum reactor 11. As shown in FIG. 1, the diffuser portion 17 has a series of sections 18 a-18 d, each one having progressively higher diameter than the previous section 18. Preferably, transition regions 20 a-c provide a gradual increase in diameter from one section 18 to the next. One of skill in the art will recognize that the diffuser portion may have greater or fewer sections 18 than shown in the figure. The elastomer composite coagulum emerges from diffuser portion 17 as “masterbatch crumb”.

In one embodiment, the masterbatch crumb is passed from coagulum reactor 11 to a de-watering extruder via a simple gravity drop or other suitable apparatus known to those of skill in the art. The dewatering extruder may bring the elastomer composite from, e.g., approximately 70-85% water content, to a desired water content, e.g., approximately 1% to 20% water content. The optimal water content may vary with the elastomer employed, the type of filler, and the desired downstream processing procedure. Suitable de-watering extruders are well known and commercially available from, for example, the French Oil Mill Machinery Co. (Piqua, Ohio, USA).

After de-watering, the resulting dewatered coagulum may be dried. In certain embodiments, the dewatered coagulum is simply thermally dried. Preferably, the dewatered coagulum is mechanically masticated while drying. For example, the dewatered coagulum may be mechanically worked with one or more of a continuous mixer, an internal mixer, a twin screw extruder, a single screw extruder, or a roll mill. Suitable masticating devices are well known and commercially available, including for example, a Unimix Continuous Mixer and MVX (Mixing, Venting, eXtruding) Machine from Farrel Corporation of Ansonia, Conn., a long continuous mixer from Pomini, Inc., a Pomini Continuous Mixer, twin rotor corotating intermeshing extruders, twin rotor counterrotating non-intermeshing extruders, Banbury mixers, Brabender mixers, intermeshing-type internal mixers, kneading-type internal mixers, continuous compounding extruders, the biaxial milling extruder produced by Kobe Steel, Ltd., and a Kobe Continuous Mixer. Alternative masticating apparatus suitable for use with various embodiments of the invention will be familiar to those of skill in the art. Exemplary methods for mechanically masticating dewatered composite are disclosed in U.S. Pat. Nos. 6,929,783 and 6,841,606, and PCT Application No. U.S. Ser. No. 09/000,732, the contents of all of which are incorporated herein by reference.

In certain embodiments, additives can be combined with the dewatered coagulum in the mechanical mixer. Specifically, additives such as filler (which may be the same as, or different from, the filler used in the coagulum reactor; exemplary fillers include silica and zinc oxide, with zinc oxide also acting as a curing agent), other elastomers, other or additional masterbatch, antioxidants, antiozonants, plasticizers, processing aids (e.g., stearic acid, which can also be used as a curing agent, liquid polymers, oils, waxes, and the like), resins, flame-retardants, extender oils, lubricants, and a mixture of any of them, can be added in the mechanical mixer. In certain other embodiments, additional elastomers can be combined with the dewatered coagulum to produce elastomer blends. Exemplary elastomers include, but are not limited to, rubbers, polymers (e.g., homopolymers, copolymers and/or terpolymers) of 1,3-butadiene, styrene, isoprene, isobutylene, 2,3-dialkyl-1,3-butadiene, where alkyl may be methyl, ethyl, propyl, etc., acrylonitrile, ethylene, and propylene and the like. Methods of producing masterbatch blends are disclosed in our commonly owned U.S. Pat. Nos. 7,105,595, 6,365,663, and 6,075,084. Alternatively or in addition, traditional compounding techniques may be used to combine vulcanization agents and other additives known in the art with the dewatered coagulum or, where a masticating apparatus is used to dry the material, the resulting masticated masterbatch, depending on the desired use.

The mixing portion 10 of the coagulum reactor 11 may be configured in several ways. FIG. 2A shows an exemplary configuration in which materials emerging from filler feed line 212, first latex feed line 214, and second latex feed line 216 all combine with one another substantially simultaneously. The angle beta between first latex feed line 214 and filler feed line 212 and the angle beta′ between second latex feed line 216 and filler feed line 212 may be varied independently. Either of these angles may vary from greater than 0° to less than 180°. Preferably, beta and beta′ are varied independently from 30° to 90°. The optimal angle may be determined in part by the relative flow rates of the three fluids and their compositions.

The angle alpha between the two latex feed lines may also be varied from greater than 0° to less than 180° (FIG. 3). Alternatively or in addition, a plurality of latex feed lines may be used for either or both of the first and second elastomer latex streams.

Alternatively or in addition, the injection points of the two latices may be staggered with respect to the injection of the filler slurry (FIG. 2B). For example, the outlet of first latex feed line 214 and second latex feed line 216 may be spaced by a distance x.

Preferably, the first elastomer latex is prepared from a natural rubber latex.

The term “diene” elastomer or “diene” rubber (elastomer and rubber are well known to be synonymous terms) should be understood as meaning, in a known way, an (one or more are understood) elastomer resulting at least in part (i.e., a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds which may or may not be conjugated).

These diene elastomers can be classified into two categories: “essentially unsaturated” or “essentially saturated”. The term “essentially unsaturated” is understood to mean generally a diene elastomer resulting at least in part from conjugated diene monomers having a level of units of diene origin (conjugated dienes) which is greater than 15% (mol %); thus it is that diene elastomers such as butyl rubbers or copolymers of dienes and of α-olefins of EPDM type do not come within the preceding definition and can in particular be described as “essentially saturated” diene elastomers (low or very low level of units of diene origin, always less than 15%). In the category of “essentially unsaturated” diene elastomers, the term “highly unsaturated” diene elastomer is understood to mean in particular a diene elastomer having a level of units of diene origin (conjugated dienes) which is greater than 50%.

Thus natural rubber belongs to the category of “highly unsaturated” diene elastomer. Exemplary natural rubber latices include but are not limited to field latex, latex concentrate (produced, for example, by evaporation, centrifugation or creaming), skim latex (a by-product of the centrifugation of natural rubber latex) and blends of any two or three of these in any proportion. The latex should be appropriate for the intended purpose or application of the final rubber product. The latex is provided typically in an aqueous carrier liquid. Selection of a suitable latex or blend of latices will be well within the ability of those skilled in the art given the benefit of the present disclosure and the knowledge of selection criteria generally well recognized in the industry.

The natural rubber latex may also be chemically modified in some manner. For example, it may be treated to chemically modify or reduce various non-rubber components, or the rubber molecules themselves may be modified with various monomers or other chemical groups such as chlorine. Exemplary methods of chemically modifying natural rubber latex are disclosed in European Patent Publications Nos. 1489102, 1816144, and 1834980, Japanese Patent Publications Nos. 2006152211, 2006152212, 2006169483, 2006183036, 2006213878, 2006213879, 2007154089, and 2007154095, U.S. Pat. Nos. 6,841,606 and 7,312,271, and U.S. Patent Publication No. 2005-0148723. Other methods known to those of skill in the art may be employed as well. Preferably, the second elastomer latex is prepared using synthetic latex. Synthetic diene elastomer of the composition in accordance with the invention is preferably chosen from the group of the highly unsaturated diene elastomers consisting of polybutadienes (abbreviated to “BR”), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers and the mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene/styrene copolymers (SBR), isoprene/butadiene copolymers (BIR), isoprene/styrene copolymers (SIR) and isoprene/butadiene/styrene copolymers (SBIR).

The elastomers can, for example, be block, random, sequential or microsequential elastomers and can be prepared in dispersion or in solution; they can be coupled and/or star-branched or also functionalized with a coupling and/or star-branching or functionalization agent. For coupling with carbon black, mention may be made, for example, of functional groups comprising a C—Sn bond or of aminated functional groups, such as benzophenone, for example; for coupling with a reinforcing inorganic filler, such as silica, mention may be made, for example, of silanol functional groups or polysiloxane functional groups having a silanol end (such as described, for example, in U.S. Pat. No. 6,013,718), of alkoxysilane groups (such as described, for example, in U.S. Pat. No. 5,977,238), of carboxyl groups (such as described, for example, in U.S. Pat. No. 6,815,473 or US 2006/0089445) or of polyether groups (such as described, for example, in U.S. Pat. No. 6,503,973). Mention may also be made, as other examples of such functionalized elastomers, of elastomers (such as SBR, BR, NR or IR) of the epoxidized type.

The following are preferably suitable: polybutadienes, in particular those having a content of 1,2-units of between 4% and 80% or those having a content of cis-1,4-units of greater than 80%, polyisoprenes, butadiene/styrene copolymers in particular those having a styrene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content of 1,2-bonds of the butadiene part of between 4% and 65% and a content of trans-1,4-bonds of between 20% and 80%, butadiene/isoprene copolymers, in particular those having an isoprene content of between 5% and 90% by weight and a glass transition temperature (“Tg”—measured according to ASTM D 3418-82) of −40° C. to −80° C., or isoprene/styrene copolymers, in particular those having a styrene content of between 5% and 50% by weight and a Tg of between −25° C. and −50° C.

In the case of butadiene/styrene/isoprene copolymers, those having a styrene content of between 5% and 50% by weight and more particularly of between 10% and 40%, an isoprene content of between 15% and 60% by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly of between 20% and 40%, a content of 1,2-units of the butadiene part of between 4% and 85%, a content of trans-1,4-units of the butadiene part of between 6% and 80%, a content of 1,2-plus 3,4-units of the isoprene part of between 5% and 70% and a content of trans-1,4-units of the isoprene part of between 10% and 50%, and more generally any butadiene/styrene/isoprene copolymer having a Tg of between −20° C. and −70° C., are suitable in particular.

While it is expected that random copolymers will be more commonly exploited, emulsions of block copolymers are also suitable for use according to the teachings herein. In some embodiments, it may be desirable to inject a coagulant, for example, a salt or acid solution, along with the latex stream, to promote coagulation of the elastomer.

The particulate filler fluid may be a carbon black slurry or any other suitable filler in a suitable carrier fluid. Selection of the carrier fluid will depend largely upon the choice of particulate filler and upon system parameters. Both aqueous and non-aqueous liquids may be used, with water being preferred in many embodiments in view of its cost, availability and suitability of use in the production of carbon black and certain other filler slurries. Small amounts of water-miscible organic solvents may also be included in aqueous carrier fluids.

Selection of the particulate filler or mixture of particulate fillers will depend largely upon the intended use of the elastomer masterbatch product. As used here, particulate filler can include any material which is appropriate for use in the masterbatch process. Suitable particulate fillers include, for example, conductive fillers, reinforcing fillers, fillers comprising short fibers (typically having an L/D aspect ratio less than 40), flakes, etc. In addition to carbon black and silica-type fillers, discussed in more detail below, fillers can be formed of clay, glass, polymer, such as aramid fiber, etc. It is expected that any filler suitable for use in elastomer compositions may be incorporated into elastomer composites according to various embodiments of the invention. Of course, blends of the various particulate fillers discussed herein may also be used.

When a carbon black filler is used, selection of the carbon black will depend largely upon the intended use of the elastomer masterbatch product. Optionally, the carbon black filler can include also any material which can be slurried and combined with a latex. Exemplary particulate fillers include but are not limited to carbon black, fumed silica, precipitated silica, coated carbon black, chemically functionalized carbon blacks, such as those having attached organic groups, and silicon-treated carbon black, either alone or in combination with each other. Exemplary carbon blacks include ASTM N100 series—N900 series carbon blacks, for example N100 series carbon blacks, N200 series carbon blacks, N300 series carbon blacks, N700 series carbon blacks, N800 series carbon blacks, or N900 series carbon blacks. Carbon blacks sold under the Regal®, Black Pearls®, Spheron®, Sterling®, and Vulcan® trademarks available from Cabot Corporation, the Raven®, Statex®, Furnex®, and Neotex® trademarks and the CD and HV lines available from Columbian Chemicals, and the Corax®, Durax®, Ecorax®, and Purex® trademarks and the CK line available from Evonik (Degussa) Industries, and other fillers suitable for use in rubber or tire applications, may also be exploited for use with various embodiments. Suitable chemically functionalized carbon blacks include those disclosed in International Application No. PCT/US95/16194 (WO 96/18688), the disclosure of which is hereby incorporated by reference.

Both silicon-coated and silicon-treated carbon blacks may be employed in various embodiments. In silicon-treated carbon black, a silicon containing species such as an oxide or carbide of silicon is distributed through at least a portion of the carbon black aggregate as an intrinsic part of the carbon black. Conventional carbon blacks exist in the form of aggregates, with each aggregate consisting of a single phase, which is carbon. This phase may exist in the form of a graphitic crystallite and/or amorphous carbon, and is usually a mixture of the two forms. Carbon black aggregates may be modified by depositing silicon-containing species, such as silica, on at least a portion of the surface of the carbon black aggregates. The result may be described as silicon-coated carbon blacks.

The materials described herein as silicon-treated carbon blacks are not carbon black aggregates which have been coated or otherwise modified, but actually represent a different kind of aggregate having two phases. One phase is carbon, which will still be present as graphitic crystallite and/or amorphous carbon, while the second phase is silica (and possibly other silicon-containing species). Thus, the silicon-containing species phase of the silicon-treated carbon black is an intrinsic part of the aggregate; it is distributed throughout at least a portion of the aggregate. A variety of silicon-treated blacks are available from Cabot Corporation under the name Ecoblack™. It will be appreciated that the multiphase aggregates are quite different from the silica-coated carbon blacks mentioned above, which consist of pre-formed, single phase carbon black aggregates having silicon-containing species deposited on their surface. Such carbon blacks may be surface-treated in order to place a silica functionality on the surface of the carbon black aggregate as described in, e.g., U.S. Pat. No. 6,929,783.

One or more additives also may be pre-mixed, if suitable, with the particulate slurry or with either the first or second elastomer latex fluids or may be combined with the mixture of these during coagulation. Additives also can be mixed into the coagulum. Numerous additives are well known to those skilled in the art and include, for example, antioxidants, antiozonants, plasticizers, processing aids (e.g., liquid polymers, oils and the like), resins, flame-retardants, extender oils, lubricants, and a mixture of any of them. Exemplary additives include but are not limited to zinc oxide and stearic acid. The general use and selection of such additives is well known to those skilled in the art.

The ratio of the dry rubber contents of the first and second elastomers (i.e., the amount of rubber contributed to the coagulum by the first and second elastomer latices) may be adjusted by adjusting the relative flow rates of the two elastomers, by diluting one of the two elastomer latices, e.g., with water and/or skim latex, or both. Other variables that may be manipulated to optimize the filler loading include the absolute flow rate of the elastomer latex streams and filler slurry (e.g., the production rate) and the relative flow rate of the elastomer latex streams and filler slurry (e.g., the filler loading).

The amount of filler in the elastomer composite may be any amount of filler that is used to make elastomer composites. For example, rubbers may be produced with at least 30 parts per hundred of rubber (phr), at least 40 phr, at least 50 phr, at least 55 phr, at least 60 phr, at least 65 phr at least 70 phr, at least 75 phr, at least 80 phr, at least 85 phr, at least 90 phr, at least 95 phr, or at least 100 phr of filler.

The invention also concerns the use of resulting elastomer composite blend accordingly to any of the mentioned embodiments for the fabrication of tires, in particular for the compositions of tire treads, tire sidewalls, wire-skim for tires, carcass and cushion gum for retread tires.

The rubber compositions of the invention also comprise all or a portion of the usual additives generally used in the elastomer compositions intended for the manufacture of treads for tyres, in particular for winter tyres, such as, for example, protection agents, such as antiozone waxes, chemical antiozonants, antioxidants, reinforcing resins, methylene acceptors (for example phenolic novolak resin) or methylene donors (for example HMT or H3M), a crosslinking system based either on sulphur or on donors of sulphur and/or peroxide and/or bismaleimides, vulcanization accelerators, or vulcanization activators.

These compositions can also comprise coupling activators when a coupling agent is used, agents for covering the inorganic filler or more generally processing aids capable, in a known way, by virtue of an improvement in the dispersion of the filler in the rubber matrix and of a lowering of the viscosity of the compositions, of improving their property of processing in the raw state; these agents are, for example, hydrolysable silanes, such as alkylalkoxysilanes, polyols, polyethers, amines, or hydroxylated or hydrolysable polyorganosiloxanes.

The rubber compositions of the invention are further processed in appropriate mixers using two successive preparation phases according to a general procedure well known to a person skilled in the art: a first phase of thermomechanical working or kneading (sometimes described as “non-productive” phase) at high temperature, up to a maximum temperature of between 130° C. and 200° C., preferably between 145° C. and 185° C., followed by a second phase of mechanical working (sometimes described as “productive” phase) at a lower temperature, typically of less than 120° C., for example between 60° C. and 100° C., finishing phase during which the crosslinking or vulcanization system is incorporated.

The crosslinking system proper is preferably based on sulphur and on a primary vulcanization accelerator, in particular on an accelerator of sulphenamide type. Added to this vulcanization system are various known secondary accelerators or vulcanization activators, such as zinc oxide, stearic acid, guanidine derivatives (in particular diphenylguanidine), and the like, incorporated during the first non-productive phase and/or during the productive phase. The level of sulphur is preferably between 0.5 and 12 phr, preferably between 1 and 10 phr, and that of the primary accelerator is preferably between 0.5 and 5.0 phr.

Use may be made, as accelerator (primary or secondary) of any compound capable of acting as accelerator of the vulcanization of diene elastomers in the presence of sulphur, in particular accelerators of the thiazoles type and their derivatives, accelerators of thiurams types, or zinc dithiocarbamates. These accelerators are more preferably chosen from the group consisting of 2-mercaptobenzothiazyl disulphide (abbreviated to “MBTS”), N-cyclohexyl-2-benzothiazolesulphenamide (abbreviated to “CBS”), N,N-dicyclohexyl-2-benzothiazolesulphenamide (“DCBS”), N-tert-butyl-2-benzothiazolesulphenamide (“TBBS”), N-tert-butyl-2-benzothiazolesulphenimide (“TBSI”), zinc dibenzyldithiocarbamate (“ZBEC”) and the mixtures of these compounds.

The final composition thus obtained is subsequently calendered, for example in the form of a sheet or of a plaque, in particular for laboratory characterization, or else extruded in the form of a rubber profiled element which can be used directly like for example tire tread.

The vulcanization (or curing) is carried out in a known way at a temperature generally of between 130° C. and 200° C. for a sufficient time which can vary, for example, between 5 and 90 min depending in particular on the curing temperature, the vulcanization system adopted and the vulcanization kinetics of the composition under consideration.

The invention relates to the rubber compositions and to the treads described above, both in the raw state (i.e., before curing) and in the cured state (i.e., after crosslinking or vulcanization).

The present invention will be further clarified by the following examples which are intended to be only exemplary in nature

Examples Carbon Black Slurry Preparation

Dry N234 carbon black (Cabot Corporation, Boston, Mass.) was mixed with water and ground to form a slurry having a concentration of about 10-15%. The slurry was fed to a homogenizer at an operating pressure of around 3000 psig such that the slurry was introduced as a jet into the mixing zone to produce a finely ground carbon black slurry. The carbon black flow rate was adjusted to about 690-1160 kg/hr to modify final carbon black loading levels. The actual carbon black loading levels were determined by nitrogen pyrolysis or thermogravimetric analysis (TGA).

Natural Rubber Latex Delivery

Field latex having a dry rubber content of about 27-31% was pumped to the mixing zone of the coagulum reactor. The latex flow rate was adjusted between about 650-720 kg/h in order to modify final carbon black loading levels and the relative proportions of natural rubber and synthetic latex.

Synthetic Latex Delivery

Styrene-butadiene latex (Nipol LX112, Zeon Corporation, Tokyo, Japan) was pumped to the mixing zone of the coagulum reactor for injection simultaneously with the natural rubber latex. The latex flow rate was adjusted between about 130-310 kg/h in order to modify final carbon black loading levels and the relative proportions of natural rubber and synthetic latex.

Carbon Black and Latex Mixing

The carbon black slurry, natural rubber latex, and synthetic latex were mixed by entraining the two latex streams into the carbon black slurry in a mixing portion of a coagulum reactor similar to that shown in FIG. 1. During the entrainment process, the carbon black was intimately mixed into the latex and the mixture coagulated.

Dewatering

The masterbatch crumb discharged from the coagulum reactor was dewatered to 10-20% moisture with a dewatering extruder (The French Oil Machinery Company, Piqua, Ohio). In the extruder, the masterbatch crumb was compressed, and water squeezed from the crumb was ejected through a slotted barrel of the extruder.

Drying and Cooling

The dewatered coagulum was dropped into a continuous compounder (Farrel Continuous Mixer (FCM), Farrel Corporation) where it was masticated and mixed with antioxidant. The moisture content of the masticated masterbatch exiting the FCM was around 1-2%. The product was further masticated and cooled on an open mill.

Curing

The cooled elastomer composite was compounded according to the formulation in Table 4 and the procedure outlined in Table 5.

TABLE 4 Ingredient Phr Rubber 100 ZnO 4 Stearic acid 2 6PPD* (antioxidant) 1.5 TBBS** (accelerator) 0.8 Sulfur 1.2 *N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine **N-tert-butyl-2-benzothiazolesulphenamide

TABLE 5 Time (min) Operation Stage 1 Farrel BR Banbury mixer (1600 cc), 75% fill factor, 80 rpm, 60° C. 0 Add rubber-carbon black masterbatch 1 Add zinc oxide, stearic acid and 6PPD 1.5 Sweep 2.5 Dump Roll mill using 4 cross-cuts and 2 end rolls Stage 2 Farrel BR Banbury mixer (1600 cc), 65% fill factor, 60 rpm, 50° C. 0 Add stage 1 compound, sulfur and accelerator 1 Dump Roll mill using 4 cross-cuts and 2 end rolls

Vulcanization was carried out in a heated press set at 150° C. for a time determined by a conventional rubber rheometer (i.e., T90+10% of T90, where T90 is the time to achieve 90% vulcanization).

Comparative Examples Dry Mixing

Dry mix elastomer blends were prepared from coagulated natural rubber and either SBR1500, a coagulated rubber available from Polimeri Europa (Milan, Italy) or coagulated Nipol LX112 (Zeon Corporation). Nipol LX112 was coagulated with 0.15 kg of aqueous 10% Ca(NO₃)₂ per kilogram of latex after adjusting the pH to 3 with 10% H₂SO₄. These materials were compounded using the formulation in Table 4, above and the procedure in Table 6.

TABLE 6 Stage 1 Fill factor (%) 75 Rotor speed (rpm) 80 Start temperature (° C.) 60 Time NR addition (s) 0 Time CB addition (s) 30 Time smalls addition (s) 150 Time for sweep (s) 60, 180 Dump time (s) 240 Stage 2 Fill factor (%) 65 Rotor speed (rpm) 60 Start temperature (° C.) 50 Time masterbatch and curatives (s) 0 Dump time (s) 60

Materials Characterization

The tensile stress of vulcanized samples (T300 and T100) were measured according to ASTM standard D-412. Tan delta 60° was determined using a dynamic strain sweep between 0.01% and 60% at 10 Hz and 60° C. Tan δ_(max) was taken as the maximum value of tan 8 within this range of strains. Rebound was measured according to ASTM standard D7121.

Tan delta 30° was measured according to the following method: specimens were prepared by curing cylinders 16 mm in diameter and 10 mm in length between parallel plates coated with a Chemlok™ bonding agent. All test specimens were allowed to equilibrate in the test laboratory for at least 24 hours prior to testing, and all were allowed to warm-up for 15-20 minutes in the rheometer at the test temperature (30° C.). Samples were first strained to 25% at 1 Hz and held at 20% steady strain for 30 s before a strain sweep from 0.1% to 30%.

Macrodispersion was determined using a disperGrader available from Alpha Technologies (Akron, Ohio) according to the manufacturer's instructions. Vulcanized rubber is cut using the cutter available from Alpha Technologies. The freshly cut surface is then analyzed for undispersed area using the pre-programmed EXP_HISTOGRAM/30 Test. The average undispersed area is reported for each sample using three scans across three different areas of the sample.

Electrical resistivity measurements were performed on wet masterbatch materials vulcanized according to CTV Method 1 and dry mix materials vulcanized according to CTV Comparative Method 1. After curing, the sheets produced from both wet masterbatch materials and dry mixed materials were rested for at least 24 hours. FIG. 4 shows the configuration of samples for electrical testing. Sheets 300 measuring 150 mm by 70 mm were measured at four points close to the points 305 for electrical contact. Both surfaces of the sample were cleaned by wiping with isopropyl alcohol, following which the sample was only handled with gloves. Silver paint was applied to both ends 310 a of the sample and as two strips 310 b near the center of the sample. A template was used to apply the center strips 310 b of conductive paint. After the paint dried, the template was removed. The prepared sample was placed on a flat, non-conductive base, and current supply electrodes were attached by metal bars at each end of the sheet. Gold electrodes were lowered onto the center paint strips with their closest edges spaced exactly 10 mm apart using a spring-loaded device that applied constant load. These were used for voltage measurement. A signal generator was used to apply pulses of 50 ms duration, with a gap of 50 ms between pulses. The direction of the current was reversed for each pulse. The current was increased for each successive pulse and the voltage measured each time. The initial current and size of the current increments were chosen such that at least 50 data points were obtained over an output range of 0-10 V. The results were first checked to ensure that voltage was proportional to current. The resistance was then obtained from a linear regression of a plot of voltage against current. The measured resistance was converted to resistivity by multiplying it by the average sample thickness and dividing the result by the distance between the center electrodes (10 mm). All compounds were tested in triplicate, and the average result was used.

Results

Table 7 shows the values of T300/T100, tan delta, and macrodispersion for vulcanizates of wet masterbatch samples and dry mixed samples prepared as described above.

TABLE 7 SBR tan tan Loading content T300/ delta delta Undispersed Masterbatch (phr) (wt %) T100 (60°) (30°) Rebound area (%) Wet 39 20 5.73 0.176 0.179 53.6 0.06 masterbatch 55 30 5.87 0.246 0.267 40.0 0.08 57 36 5.87 0.252 0.282 38.6 0.04 Dry mix (NR + 39 20 5.17 0.168 0.182 52.2 0.44 SBR1500 55 30 5.10 0.235 0.268 42.8 0.14 57 36 5.06 0.236 0.273 42.2 0.16 Dry mix (NR + 39 20 4.83 0.168 0.189 49.5 1.21 Zeon SBR) 55 30 4.76 0.242 0.294 38.1 1.07 57 36 4.48 0.256 0.308 37.3 0.69

The wet masterbatch materials exhibit superior microdispersion with respect to the dry mixed samples. This is reflected in the values of T300/T100 for the wet masterbatch and dry mixed samples. The superior performance of the wet masterbatch samples reflects the superior interaction and dispersion of the carbon black filler with respect to the elastomer.

FIG. 5 compares the resistivity of a number of samples, including dry mixed and wet masterbatch materials produced with only natural rubber latex, blends prepared by dry mixing SBR with a wet masterbatch material produced with natural rubber latex, and blends prepared by the wet masterbatch method described in the Examples. The masterbatches including only natural rubber latex were compounded using cyclohexyl benzothiazole sulfenamide (CBS) as the accelerator rather than TBBS. The difference in resistivity between these vulcanizates and vulcanizates prepared using TBBS as the accelerator is expected to be small. The results show that the resistivity of wet mix elastomer composite blends is higher than that of dry mix elastomer composite blends. In addition, the resistivity of both wet and dry mix elastomer composite blends is greater than that of the corresponding composites produced with only natural rubber latex.

The foregoing description of preferred embodiments of the present invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings, or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. 

1. A process for preparing a tire comprising a rubber composition based on at least an elastomer composite, wherein the elastomer composite is prepared by a method comprising: feeding a continuous flow of a first fluid comprising a first elastomer latex to a mixing zone of a coagulum reactor; feeding a continuous flow of a second fluid comprising a second elastomer latex to the mixing zone; feeding a continuous flow of a third fluid comprising a particulate filler slurry to the mixing zone; allowing the first elastomer latex and the second elastomer latex to coagulate with the particulate filler; and discharging a flow of elastomer composite from a discharge end of the coagulum reactor, wherein the first elastomer latex and the second elastomer latex are incompatible.
 2. The process according to claim 1, wherein the first fluid and the second fluid combine with the third fluid to form a mixture, and wherein the first fluid and the second fluid combine with the third fluid substantially simultaneously.
 3. The process according to claim 1, wherein the first fluid and the third fluid combine to form a mixture, and wherein the second fluid combines with the mixture.
 4. The process according to claim 1, wherein the first elastomer latex comprises a natural rubber latex.
 5. The process according to claim 1, wherein the second elastomer latex comprises a synthetic elastomer latex.
 6. The process according to claim 1, wherein the particulate filler comprises carbon black.
 7. The process according to claim 4, wherein the second elastomer latex comprises a synthetic elastomer latex, and wherein the elastomer composite includes natural rubber and about 1 to about 36 wt % styrene-butadiene rubber with respect to the total rubber content.
 8. The process according to claim 7, wherein the elastomer composite includes natural rubber and about 20 to about 36 wt % styrene-butadiene rubber with respect to the total rubber content.
 9. The process according to claim 1, wherein the elastomer composite exhibits a macrodispersion of less than 0.1% undispersed area.
 10. A process for preparing a tire tread having a rubber composition based on at least an elastomer composite, wherein the elastomer composite is prepared by a method comprising: feeding a continuous flow of a first fluid comprising a first elastomer latex to a mixing zone of a coagulum reactor; feeding a continuous flow of a second fluid comprising a second elastomer latex to the mixing zone; feeding a continuous flow of a third fluid comprising a particulate filler slurry to the mixing zone; and allowing the first elastomer latex and the second elastomer latex to coagulate with the particulate filler; and discharging a flow of elastomer composite from a discharge end of the coagulum reactor, wherein the first elastomer latex and the second elastomer latex are incompatible.
 11. The process according to claim 10, wherein the first fluid and the second fluid combine with the third fluid to form a mixture, and wherein the first fluid and the second fluid combine with the third fluid substantially simultaneously.
 12. The process according claim 10, wherein the first fluid and the third fluid combine to form a mixture, and wherein the second fluid combines with the mixture.
 13. The process according to claim 10, wherein the first elastomer latex comprises a natural rubber latex.
 14. The process according to claim 10, wherein the second elastomer latex comprises a synthetic elastomer latex.
 15. The process according to claim 10, wherein the particulate filler comprises carbon black. 